Program: GS-2011B-Q-13

Transmission spectroscopy is a technique allowing a direct probe of the atmospheres of transiting extrasolar planets. Recent discoveries of bright targets with rich fields of comparison stars should allow ground based observatories to make precision spectroscopic measurements previously limited to space-based observatories. Indeed this has been recently demonstrated using VLT/FORS2 - a multi-object spectrograph with capabilities similar to GMOS. We propose to obtain time-series spectra of the exoplanet system WASP-29 during a single primary transit event with GMOS, in order to probe the composition of the planet's atmosphere. Using GMOS we can simultaneously observe nearby bright comparison stars to perform differential spectro-photometry, allowing the systematics that normally limit ground based spectro-photometry to be calibrated and removed. WASP-29 is a very promising target for transmission spectroscopy, with expected transit depth variations of order 0.05% in the optical, and importantly several bright comparison stars in the GMOS field of view. We will observe a transit using the R400 grism, providing coverage from ~525-925 nm. Not only will these observations represent the first measurements of a hot-Saturn atmosphere to date, but will provide a test case to promote the use of Gemini telescopes for exoplanetology, paving the way for potentially ground breaking contributions.